In recent years, biodegradable resins typified by polylactic acid have attracted attention from the viewpoint of environmental conservation. Of the biodegradable resins, the polylactic acid is highly useful, because the polylactic acid is one of the most heat-resistant resins and less costly due to its mass-producibility. However, the polylactic acid is disadvantageously poor in moldability due to its low melt viscosity, and an object molded or formed from the polylactic acid is brittle. Addition of a soft component is a conceivable method for overcoming the brittleness, but is problematic in that the heat resistance characteristic of the polylactic acid is deteriorated.
An attempt is made to accelerate the crystallization by a heat treatment or the like for satisfying the requirements for the heat resistance and the shock resistance. Where the crystallization rate is low, the conditions for the molding and processing are considerably limited, and the impact resistance is still unsatisfactory. For increasing the crystallization rate, a crystalline nucleus agent such as talc or silica is added, but the amount of the agent to be added should be increased for satisfying the requirements for the mechanical characteristics. As a result, the molded object has an increased specific gravity and opacity and, hence, the applications thereof are limited.
On the other hand, JP-A-2000-17157 discloses a composition comprising an aliphatic polyester and an organized phyllosilicate, and a film formed of this composition. In this reference, it is stated that the mechanical strength and the heat sealability are improved by combining the aliphatic polyester with the phyllosilicate. However, no consideration is given to a molded object other than the film. Further, no practical consideration is given to a polylactic acid resin which is poor in moldability.
JP-A-2001-89646 discloses a composition comprising a biodegradable resin and an organically treated phyllosilicate. It is stated that the composition improves the rigidity and the biodegradation rate. However, no practical consideration is given to a molded object. In practice, polylactic acid of a low melting point type which is moldable at 160° C. is employed, so that the resulting resin composition has a lower heat resistance.